Abstract

Dust samples collected from former mining and urban locations around Almadén, Spain, were processed to extract their fine, respirable fraction. The Almadén area has been continuously mined for Hg since pre-Roman days and a huge amount of Hg has been recovered, with estimated original reserves of >250,000 tonnes. The main recognised environmental problem associated with Hg mining has been the progressive poisoning of workers with jobs in direct contact with Hg vapours. There is no evidence for significant contamination of the local groundwater supply, as a relative lack of pyrite in the Hg deposits has, together with an abundance of carbonates, prevented the formation of acid mine drainage. The pH of waters and soils in the area is thus typically neutral or even slightly alkaline, inhibiting the solution, transport, and reconcentration of Hg. However, the legacy of mining has left contaminated ground which, combined with a semi-arid climate, has created a potential problem of respirable Hg-bearing dust. The ground is in places heavily contaminated with Hg, both as cinnabar (HgS) and as schuetteite, Hg3(SO4)O2, a mineral formed by the oxidation of cinnabar ore exposed to sunlight but also commonly found in the bricks and remains of old Hg furnaces and condensers. Some of the contaminated sites are used to keep livestock and grow plants that are harvested for human consumption. Comparisons between unprocessed and processed dust samples show a higher incidence of Hg-bearing particles in the finer fraction. The sizes of the Hg-bearing resuspended particles in all sites varies from inhalable dust (15 µm aerodynamic diameter), through respirable dust (< 5 µm) to fine (<2.5 µm) and ultrafine (0.1 µm). Tiny condensed Hg spherules and specks are particularly small and in aerosol form would be well capable of reaching the deepest levels of the lung alveoli. The spherical particles are interpreted as mercuric sulfate vapour condensates and possibly native Hg droplets, whereas polycrystalline aggregates of silica and abundant Hg, S, and in some cases, Cl (possible corderoite Hg3S2Cl2) are probably furnace-slag aerosols. The greatest amount of contamination is directly associated with old processing plants, especially at Almadenejos, a village with 600 inhabitants. Almadén itself is a town of some 6500 inhabitants and lies adjacent to, and downwind of, the main Hg mine in the area. Dust samples collected from the University car park and the main supermarket car park both contain appreciable amounts of respirable Hg-bearing aerosols.